Vehicle body frame for motorcycle and its fabrication method

ABSTRACT

To adopt die cast products as parts of a vehicle body frame. A vehicle body frame is provided with an alumite treating, showing that brightness and appearance of pivot plates which are die cast products differ from those of non-die cast products, head pipes, longitudinal pipes and cross pipe. By carrying out a local coating treatment on the pivot plates, the pivot plates are provided with a color the same as that of the head pipe, the longitudinal pipes and the cross pipe. By making die cast products portions of constituent parts, the fabrication cost of the vehicle body frame can be reduced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a vehicle body frame for amotorcycle and a fabrication method for manufacturing the same.

[0003] 2. Description of Background Art

[0004] With reference to FIG. 7, a perspective view is illustrated of arepresentative vehicle body frame for a motorcycle. The frame 100 for amotorcycle is integrated by welding and includes a head pipe 101, upperlongitudinal pipes 102, lower longitudinal pipes 103 (one of the pipes103 is not illustrated), pivot plates 104 and a cross pipe 105.

[0005]FIG. 8 is a conventional flow diagram for fabricating a vehiclebody frame and the designation STXXX is utilized to designate aparticular step number.

[0006] ST111: The head pipe is fabricated by a gravity die castingprocess. The gravity die casting process is also simply referred to as adie casting process and is a fabrication method in which a metal mold isused in place of a sand mold, molten aluminum is injected into the metalmold and a feeding head is applied thereon. Only gravity is utilized onthe molten metal and a metal mold is used. Accordingly, the process isalso referred to as “gravity die casting.” Since the molten metalcomprises aluminum, for several tens of thousands of times it isfeasible for supplying the molten metal injection into a metal mold madeof gray cast iron (FC) or structural carbon steel. The cost of the moldcan be reduced as compared with a sand mold.

[0007] The gravity die casting is preferably adopted for parts of amotorcycle having more or less complicated shapes because gases are notentrapped and the casting surface is excellent since the injection speedis slow.

[0008] ST112: By projecting shot grains onto or buffing a provided headpipe cast article, the surface is finished.

[0009] ST113: Similar to ST111, the pivot plates are fabricated by thegravity die casting process.

[0010] ST114: By projecting shot grains onto or buffing provided pivotplates cast articles, the surfaces are finished.

[0011] ST115: Upper/lower longitudinal pipes as well as the cross pipeare fabricated by drawing or extrusion. Pipes or bars having uniformsections can be fabricated by drawing or extrusion swiftly and in massproduction.

[0012] ST116: The upper/lower longitudinal pipes and the cross pipe aresuitably cut and subjected to bending.

[0013] ST117: The above-described head pipes, upper/lower longitudinalpipes, pivot plates and cross pipe are integrated by welding.

[0014] ST118: The product is subjected to alumite treatment and ananodic oxidation coating is formed on the surface. Thereby, a beautifulvehicle body frame can be fabricated.

[0015] However, according to the gravity die casting, as mentionedabove, the injection speed is slow and accordingly, the productivity islow which hinders a reduction in fabrication cost of the vehicle bodyframe.

OBJECTS AND SUMMARY OF THE INVENTION

[0016] Hence, it is an object of the present invention to achieve areduction in fabrication cost of the vehicle body frame by improving theconstitution and the fabrication method.

[0017] According to the present invention, a vehicle body frame for amotorcycle is constituted of integrating pipes made of aluminum and aplurality of aluminum cast parts by welding. The portions or the totalof the plurality of aluminum cast parts are die cast products.

[0018] A die cast product is excellent in the production efficiency,resulting in achieving low cost of a cast product. Hence, by making thedie cast products portions of constituent parts, the fabrication cost ofa vehicle body frame is reduced.

[0019] According to the present invention, a vehicle body frame for amotorcycle is fabricated by the steps of integrating aluminum series diecast products and aluminum series non-die cast products fabricated by amethod other than die casting, subjecting an integrated article to analumite treating and coating only die cast portions.

[0020] A state of the skin is deteriorated in a die cast product incomparison with a non-die cast product. Therefore, when alumite treatingis completed, a die cast portion of an alumite coating does not have asgood an appearance as compared with other portion thereof. Hence, theappearance of the vehicle body frame is maintained by coating only thedie cast portion.

[0021] Further scope of applicability of the present invention willbecome apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

[0023]FIG. 1 is an exploded view of a vehicle body frame for amotorcycle according to the present invention;

[0024]FIG. 2 is a fabrication flow diagram of a vehicle body frame for amotorcycle according to the present invention;

[0025]FIG. 3 illustrates views showing the vehicle body frame accordingto the present invention;

[0026]FIG. 4 is a graph investigating a relationship between gate speedand a material gas amount;

[0027]FIG. 5 is a graph showing a relationship between the gate speedand proof strength;

[0028]FIG. 6 is a graph showing a relationship between the gate speedand tensile strength;

[0029]FIG. 7 is a perspective view of a representative vehicle bodyframe for a motorcycle; and

[0030]FIG. 8 is a fabrication flow diagram of a conventional vehiclebody frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] An explanation will be given as follows of an embodiment of thepresent invention in reference to attached drawings. FIG. 1 is adisassembled view of a vehicle body frame for a motorcycle according tothe present invention. The vehicle body frame 10 for a motorcyclecomprises a head pipe 11, upper longitudinal pipes 12, lowerlongitudinal pipes 13, pivot plates 14 and a cross pipe 15.

[0032]FIG. 2 is a fabrication flow diagram of the vehicle body frame fora motorcycle according to the present invention and STXX designates astep number.

[0033] Further, the method of fabricating the head pipe, the upper/lowerlongitudinal pipes and the cross pipe is the same as described in theconventional technology and a special devise is needed in the method offabricating the pivot plates.

[0034] STO 1: The head pipe is fabricated by the gravity die castingprocess. Although an explanation of the gravity die casting process willbe omitted since a detailed explanation thereof has been given in adescription of the conventional technology, gases are not entrapped andthe casting surface becomes excellent since the injection speed is slow.

[0035] ST02: By projecting shot grains onto or buffing the provided headpipe cast article, the surface is finished.

[0036] ST03: The upper/lower longitudinal pipes and the cross pipe arefabricated by drawing or extrusion. Pipes or bars having uniformsections can be fabricated by drawing or extrusion swiftly and in massproduction.

[0037] ST04: The upper/lower longitudinal pipes and the cross pipe aresuitably cut and subjected to bending.

[0038] ST05: The pivot plates are fabricated by a die cast castingmethod, described later. The die cast casting method is a fabricationmethod in which molten aluminum is injected into a cavity under highpressure. Accordingly, the production efficiency is excellent and alarge amount of cast products can be fabricated at a low cost.

[0039] ST06: By projecting shot grains onto or buffing the providedpivot plate cast articles, the surfaces are finished.

[0040] ST07: The above-described head pipe, upper/lower longitudinalpipes, pivot plates and cross pipe are integrated by welding.

[0041] ST08: The product is subjected to the alumite treatment and ananodic oxide film is formed on the surface.

[0042] ST 09: Only the pivot plates are subjected to coating, mentionedlater. Thereby, a beautiful vehicle body frame can be fabricated.

[0043] FIGS. 3(a) and 3(b) are views showing the vehicle body frameaccording to the present invention.

[0044]FIG. 3(a) shows the vehicle body frame 10 after the ST08 (alumitetreatment), showing that the brightness and appearance differ at thepivot plates 14 in comparison with other portions (head pipe 11,longitudinal pipes 12, 13 and cross pipe 15).

[0045]FIG. 3(b) shows the vehicle body frame 10 after the ST09 (localcoating treatment), showing that the color of the pivot plates 14 lookslike the color of other portions (head pipe 11, longitudinal pipes 12,13 and cross pipe 15).

[0046] A detailed explanation will be given of die casting and coatingwhich are features of the present invention.

[0047] In the die casting, the casting speed is extraordinarily higherthan those of sand mold casting and metal mold casting. Accordingly,entrapping of gasses is significant, resulting in the roughening of thecasting surface, and the entrapped gases remain in the form of airbubbles, resulting in the air bubbles are broken by welding heat.

[0048] Hence, there is carried out an experiment to establish a diecasting method adaptable to the present invention as a premise ofcompleting the present invention.

[0049] Experimental conditions:

[0050] (1) Composition of test sample; aluminum alley die cast 6 series(JIS H 5302) TABLE 1 Chemi- cal Chemical components symbol Cu Mg Zn FeMn Ni Sn Al ADC6 0.1 1.0 2.5- 0.4 0.8 0.4- 0.1 0.1 bal- or or 4.0 or or0.6 or or ance less less less less less less

[0051] (2) Injection temperature; 730° C.

[0052] (3) Caster; ordinary die casting machine

[0053] (4) Gate speed; 5-65 m/s

[0054] (5) Gate sectional area; 9.75 cm²

[0055]FIG. 4 is a graph illustrating a relationship between gate speedand a material gas amount in which a gas amount in a material (castproduct) is illustrated by changing the gate speed in the experiment.The abscissa designates the gate speed and the ordinate designates thegas amount per 100 g of aluminum.

[0056] According to the graph, it is known that when the gate speedexceeds 15 m/s, the gas amount rapidly increases.

[0057]FIG. 5 is a graph showing a relationship between the gate speedand proof strength and FIG. 6 is a graph showing a relationship betweenthe gate speed and tensile strength.

[0058] It is known that as has been explained in reference to FIG. 4,when the gate speed exceeds 15 m/s, the gas amount increases rapidly andtherefore, the gases remains as air bubbles. When the gate speed exceeds15 m/s in FIG. 5 and FIG. 6, both the proof strength and the tensilestrength are remarkably reduced.

[0059] It is known from the explanation that in the aluminum alloy diecasting, by restraining the gate speed to 15 m/s, entrapping of gassescan significantly be reduced. It is prospected that if gasses are notentrapped, the casting surface becomes fine compared with that of aconventional die cast product and the invented die cast product can bewelded since there are no air bubbles.

[0060] Further, although detailed data will be omitted, when the gatespeed becomes lower than 5 m/s, molten metal is cooled in a procedure ofbeing filled in the cavity, resulting in a short run when molding.

[0061] Hence, it is preferable to set the gate speed to 5-15 m/s.

[0062] Next, an explanation will be given of coating.

[0063] There is adopted a coating whose color is the same as that ofalumite coating when the coating is dried and providing a cross linkedcoating dried at room temperature. In the case of “cross linked coating”the coating strength is large and therefore, there is no concern ofpeeling of the coating. Further, since “normal temperature drying” iscarried out, heated drying is not needed. If the heated drying iscarried out, the alumite coating is impaired. Because the heated dryingis not needed, a number of coating steps can be reduced and an increasein the fabrication cost can be restrained.

[0064] Accordingly, the cross linked coating dried at room temperatureis carried out in order to achieve protection of alumite and maintenanceof coating.

[0065] Further, the aluminum cast parts according to the presentinvention are the head pipe and the pivot plates according to theembodiment and the die cast products among them are the pivot plates.However, the present invention is not limited to this example, but thealuminum cast parts and the die cast articles may be any of membersconstituting the vehicle body frame for a motorcycle.

[0066] The aluminum series die cast products according to the presentinvention are the pivot plates according to the embodiment and thealuminum series non-die cast products are the head pipe, thelongitudinal pipes and the cross pipe. However, the present invention isnot limited to this example, but the aluminum series die cast productsmay be any of members constituting the vehicle body frame for amotorcycle.

[0067] Further, the longitudinal pipes or the cross pipe may be providedwith any of a round section, a rectangular section or other noncircularsection.

[0068] Further, aluminum here includes aluminum alloy.

[0069] The present invention achieves the following effects by theabove-described constitution.

[0070] According to the present invention, in a vehicle body frame for amotorcycle including integrating pipes made of aluminum and a pluralityof aluminum cast parts by welding, portions or a total of the pluralityof aluminum cast parts are die cast products. Since the die castproducts are provided with excellent production efficiency, a low costof die cast products can be achieved. By making the die cast productsportions of constituent parts, a reduction in the fabrication cost ofthe vehicle body frame can be achieved.

[0071] According to the present invention, coating die cast portions areadopted in portions of the vehicle body frame. After the alumitetreatment, the die cast portions of alumite coating is not good inappearance compared with other portions thereof Hence, by coating onlythe die cast portions, the appearance of the vehicle body frame ismaintained.

[0072] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of fabricating a vehicle body frame fora motorcycle comprising the following steps: integrating aluminum seriesdie cast products and aluminum series non-die cast products fabricatedby a method other than die casting; subjecting an integrated article toan alumite treating; and coating only die cast portions.
 2. The methodof fabricating the vehicle body frame for a motorcycle according toclaim 1, and further including the step of fabricating said die castproducts with molten aluminum injected into a cavity under highpressure.
 3. The method of fabricating the vehicle body frame for amotorcycle according to claim 2, and further including the stops of diecasting pivot plates for the vehicle body frame and projecting shotgrain onto the pivot plates for finishing the surface.
 4. The method offabricating the vehicle body frame for a motorcycle according to claim1, where in a gate speed for the die casting is 5-15 m/s for the moltenmetal.